The present invention relates to a shock absorber comprising a cylinder section and a piston section that van be moved therein, the piston section and cylinder section each being provided with fixings for connection with the parts that can be moved with respect to one another and said piston section being sealed with respect to said cylinder section in order to delimit chambers on either side thereof, a firsts chamber close to the fixing of said piston section and a second chamber close to the fixing of said cylinder section, a connecting channel being arranged between said chambers for connecting said chambers, said connecting channel containing a valve assembly for influencing the fluid steam through said connecting channel, comprising a valve seat and a part that can move with respect thereto under liquid pressure and seals off the valve seat, said movable part of the valve assembly forms a boundary wall of an auxiliary chamber, said auxiliary chamber being provided with an inlet which, viewed in the direction of the movement of the fluids opens upstream of said valve assembly.
Shock absorbers of this type are generally known in the art. These are used in a wide variety of vehicles, the aim being to adapt the damping characteristics to the driving conditions. Auxiliary flow channels and main flow channels are employed. En the case of minor liquid movement damping can take place in the auxiliary flow channel, whilst in the case of more substantial liquid movements in the shock absorber the main flow channel with its own damping characteristics is also effective. These constructions react directly to the liquid movement, that is to say corresponding to the speed of movement of piston and cylinder section with respect to one another, the various valves are opened and closed. A frequency-dependent control by means of retarding the damping characteristics with respect to the mutual movement of piston/cylinder by hydraulic means is not known.
Electronic controls have been proposed in the art for providing an electronic delay in the build-up of force. That is to say, in the case of a large number of movements in rapid succession the damping is restricted, whilst more damping occurs in the case of a movement of longer duration. Although they are effective, electronic controls of this type are of particularly complex construction. Particularly rapid sensors, computation units and actuators are needed to enable the valves present to react sufficiently quickly.
A device with which a ball can be moved in an auxiliary chamber is described in U.S. Pat. No. 4,660,686. In the rest position this ball assumes a position such that the volume of the auxiliary chamber is maximum. This ball beans on a spring plate, which sprig plate is able to close off an opening located beneath it. When pressure is applied in the direction in which the spring plate opens, pressure is also applied to the rear of the ball. Because the diameter of the ball is greater than the diameter of the opening close to the valve plate, with identical pressure the force of the ball on the valve plate will be greater and the valve plate will closed. A relief valve is present in the liquid feed channel to the rear of the ball and when a specific value is exceeded this relief valve will open, as a result of which the pressure on the rear of the ball decreases and the valve plate will thus be opened to a greater or lesser extent. That is to say, depending on the pressure in the system, the valve plate will be open to a greater or lesser extent. This reaction is immediate, that is to say without any delay.
In U.S. Pat. No. 5,392,883 a device is described consisting of an auxiliary chamber in which there is an opening with a valve under slight spring pressure which operates in one direction, which valve is also provided with an opening, which, however, has a smaller passageway. In the rest position the volume of the auxiliary chamber is minimum. Here again, adjustment of the flow opening takes place immediately (delay of at most a few milliseconds) in response to the pressure conditions.